钙长辉长无球粒陨石NWA 11592的岩石矿物学特征及富铁橄榄石脉成因研究

The petrological and mineralogical characteristics of Eucrite NWA 11592 and the study on the genesis of the Fe⁃rich olivine veins

灶神星是太阳系最大的硅酸盐质小行星,它的岩石样品(HED族陨石)是目前太阳系最古老的岩浆岩之一,很有可能记录了类地行星最早期地质流体活动的重要信息。本次工作首次在一块非角砾岩平衡型的Eucrite NWA 11592中发现了较粗长的富铁橄榄石脉。通过对NWA 11592陨石进行详细的岩相学和地球化学特征研究,将NWA 11592陨石划为玄武质非角砾岩型Eucrite,冲击变质程度至少为S4,热变质程度为6型。NWA 11592中富铁橄榄石脉最有可能为含H_(2)O流体沿裂隙的沉淀产物,反应系统应是开放且较为氧化的(f_(O2)达IW+0.9),且应发生在灶神星浅层地壳>4 km的埋藏深度。含H_(2)O流体渗透作用除更多地发生在灶神星表面或近地表外,还有可能发生在灶神星内部的浅层地壳中。

Vesta is the largest silicate asteroid in the solar system,and its rock samples(HED meteorites)are among the oldest magmatic rocks in the solar system,possibly recording important information about the earliest geological fluid activities of terrestrial planets.For the first time in this work,a thicker and longer Fe⁃rich olivine vein was found in a piece of unbreccia equilibrium Eucrite NWA 11592.Through detailed research of petrographic and geochemical characteristics of the NWA 11592 meteorite,NWA 11592 is classified as basaltic unbreccia Eucrite,with an impact metamorphism degree of at least S4 and a thermal metamorphism degree of type 6.The Fe⁃rich olivine veins in NWA 11592 is most likely to be the precipitation products of H_(2)O⁃bearing fluids along the fractures.The reaction system should be open and relatively oxidized(f_(O2) up to IW+0.9),and it should occur at a burial depth of>4 km in the shallow crust of Vesta.The infiltration of H_(2)O⁃bearing fluids not only occurs more on the surface or near the surface of Vesta,but may also occur in the shallow crust of Vesta's interior.